1. Field of the Invention
The present invention relates to a rack, and an optical apparatus using the rack.
2. Description of the Related Art
Along with a demand for a smaller size of an optical apparatus, such as a digital still camera and a digital video camera, a lens barrel attachable to it is also required for a smaller size. For a smaller battery and a longer capture time, the power saving of the lens barrel is also required. Japanese Patent Laid-Open No. (“JP”) 2005-315935 discloses a moving mechanism that uses a motor and rack to move a lens holder frame in an optical axis direction and a helical torsion spring to force a rack against a lead screw of the motor.
In the rack configured to sandwich the lead screw using a main tooth and a holding tooth, the main tooth and holding tooth may jump from a thread of the lead screw due to the impact, such as a drop, and thereby the captured image is likely to disturb and blur. When a strong force is applied between the rack and the lead screw as proposed in JP 2005-315935 so as to prevent the tooth jump, the motor rotational load increases due to the increased frictional force between them, and the power saving of the motor would be lost or the motor and lens barrel would become larger. On the other hand, in the rack in which only the forced main tooth is engaged with the lead screw in the normal state, the opposite tooth arranged opposite to the main tooth with respect to the lead screw is engaged with the thread of the lead screw on impact, and the positional offset of the rack in the axial direction of the screw is prevented. However, when only the main tooth contacts the lead screw, it is necessary for stable movements of the rack to increase the force applied to the main tooth, and the motor rotational force increases and the motor power saving would be lost or the motor and the lens barrel would become larger.